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Ostium’s Arbitrum perp DEX loses about $18 million in oracle attack

The exploit used a compromised oracle signer key to post falsified, future-dated price reports, draining nearly one-third of Ostium’s liquidity vault.

Reported · Written up by our desk · DeFi

DeFi security firm Blockaid said Ostium, an Arbitrum-based decentralized perpetuals exchange, lost about $18 million in USDC after attackers manipulated its price data through an oracle compromise on Wednesday.

According to the firm, the attackers used a compromised oracle signer key, along with a registered PriceUpKeep forwarder and future-dated authorized oracle reports, to generate fake trading profits that triggered a large USDC payout from Ostium’s liquidity vault.

Ostium paused all trading and said it was investigating the issue with its OLP vault. At the time of the attack, the protocol had about $63 million in total value locked, meaning the drain was close to one-third of its liquidity.

The incident comes amid a heavy spell of DeFi hacks, with more than $840 million stolen from DeFi protocols in the first five months of 2026, including large losses attributed to KelpDAO and Drift Protocol, Decrypt reported. Decrypt also noted security concerns that AI is accelerating exploit discovery.

Sources